Overview
Imagine the perfect latex paint. It sticks to anything,
covers in one coat, levels smoothly, is strong yet flexible
and lasts for decades. It never fades or chalks. It discourages
mildew growth and is formulated so you can
apply it in cold weather. And it doesn't
drip. Unfortunately, that
perfect paint has yet to
be developed. Never
will be, either. The ingredients in a batch of paint just have too many limitations
and trade-offs. But while there may be no such thing
as perfect paint, there are definitely high- and low-quality
paints. Here we'll look at the differences, particularly as
they apply to exterior latex paints.
And why it's worth it to buy the
good stuff.
Figure A: High- vs. low-quality paint
Figure A: High Quality vs. Low Quality
High-quality paint
has more total solids
(pigments plus resins) and
fewer solvents than lower-quality
paint. So while the
two may go on with the
same thickness, when the
solvents evaporate, a high-quality
paint leaves a
thicker, tougher paint film.
Low-quality paint
has fewer solids and more
solvents. Once the solvents
evaporate, the thinner
paint film left behind
is less durable and doesn’t
cover as well. You’ll spend
more time and money
repainting to achieve the
performance of a high-quality
paint.
What is paint, anyway?
To most of us, one opened can of paint may look pretty
much like the next, but not to the chemists who formulate
it. A typical batch of latex base paint—the untinted
paint to which colorants are added in the store—can
contain 15 to 20 ingredients or more. Base paint
ingredients can be lumped into four categories:
Pigments are finely ground particles that give paint its
opacity and ability to “hide” the surface it’s applied to.
(Colorants are the tints added at the hardware store or
home center to produce the exact color you want.)
Resins (or binders) are the ingredients that hold the
pigments and colorants in place after the paint dries.
Solvents (also called carriers) are the liquids that
transport the above ingredients from the brush or roller
onto the wall. In latex paint the main solvent is water; in
oil-based paint it’s primarily mineral spirits. These evaporate
as the paint dries.
Additives are the chemicals that affect everything from
mildew resistance to workability.
To understand how latex paint works, picture a bathtub
full of water and Ping-Pong balls. Some Ping-Pong
balls are white, representing the pigments. Others are—let’s pick a color—red, and represent the colorants.
Some are clear and exceptionally sticky and represent
the binders. The water they’re all bobbing in is the solvent.
As the bathtub drains (that is, the paint dries), the
clear Ping-Pong balls link together, trapping the white
and red balls in a tight mesh. Bingo, there’s your paint
film. The purity, quantity and size of all those Ping-Pong balls are what dictate paint quality.
High-quality paint has better pigments, so it hides better
The predominant and most expensive pigment in paint
is titanium dioxide, a very pure white powder with
exceptional hiding qualities. High-quality paint contains
a high percentage of this pigment. Other, less expensive
pigments such as clay, silica and talc are found in
expensive paints but are more prevalent in cheap paints.
They’re not as white and pure, and they’re poorer
“hiders,” meaning you’ll need to apply more or thicker
coats of paint to cover existing colors (Fig. B). You can’t
really judge the quality of a paint by the amount of
pigment in it; for instance, flat paints always contain
more pigment than glossier paints. But you’ll certainly find better-quality pigments in expensive paints.
Figure B: Better Pigments Mean Better Coverage
Figure B: Better Pigments Mean Better Coverage
The pigments in the
high-quality paint on the
left are smaller and purer,
so they do a better job of
filling in and blocking the
color of the surface they’re
applied over
High-quality paint has better resins so it sticks better and lasts longer
Resins—sometimes called binders—are the plastic-like
ingredients in paint that bind together to create a film,
encapsulating the pigments. The best latex resins are
made of acrylic, and the best acrylic resins are made
from small particles that can deeply penetrate the wood
pores and “grab on” (Fig. C). That’s why high-quality
binders last longer and better resist blistering, peeling
and wear. At the store, you’ll usually find paint labeled
two ways: “100 percent acrylic” or “vinyl acrylic.” Buy
the higher-quality 100 percent acrylic paint.
Glossy paints contain more resins and less pigment
than flat paint; it’s the resins that make a glossy paint
glossy. But a high-quality gloss paint will have more
resins than a low-quality gloss paint, and those resins
will be higher quality. Since resins are the most expensive
component in any paint, high-quality paint with high-quality
resins is more expensive.
Figure C: Better Resins Means Better Adhesion
Figure C: Better Resins Means Better Adhesion
The resins in the high-quality paint are
smaller and better able to cling to each other
and penetrate the surface they're applied to.
This means a stronger, longer-lasting paint film.
High-quality paint has more solids
By now we know that paint sheen is determined by the
ratio of binders to pigments: Flat paint has more pigment
and less resin; glossy paint has less pigment and
more resin. But paint sheen aside, high-quality paints
will have more combined solids (pigments and resins)
and less water than cheap paints. Our expensive gallon of paint
contains as much as 45 percent solids by volume, while
cheap stuff may have less than 30 percent (Fig. A). A
higher percentage of solids means a thicker paint film,
better hiding and greater durability. The remaining
ingredient in a can of latex paint is primarily water, the
cheapest ingredient of all, with the sole purpose of carrying
the binder and pigment to the surface before evaporating.
High-quality paint has additives that improve its application and protective qualities
All latex paints contain additives, but high-quality
paints contain more or better ones that also cost more.
Thickeners, which can significantly increase the cost of
a gallon of paint, slightly slow down and smooth out
your brush stroke so you leave an even, thick coat
of paint. The high-quality latex paint now available will
brush on almost as smoothly as oil paint. Surfactants
help paint soak into the wood and adhere better as well
as help stabilize the color and viscosity of paint.
Mildewcides limit mildew growth after the paint has
been applied (at least for a few years).
Other additives protect the quality of the liquid paint
if it freezes a time or two, prevent the paint from foaming
when mixed or help the paint flow better from
brush to surface. These additives increase the cost of
high-quality paint.
The bottom line
1 of 1
100% acrylic paint
Remember, you get what you pay for.
Even if exterior latex paint ingredients were listed on the can
like the ingredients on a can of soda pop, it would be tough
comparing paints and sorting the good from the bad. We
could look for paints with more solids, higher-quality ingredients
and better additives. But we’re do-it-yourselfers, not
chemists! Paint chemists are a secretive group anyway; they
do a lot of research and testing and don’t like other paint
chemists knowing their paint recipes.
So most experts—both chemists and pro painters—will
just tell you this: Buy paint that’s 100 percent acrylic, and
buy paint that’s expensive (preferably on sale). You’ll get
more for your money and labor! A high-quality exterior latex
paint can last 10 years or more, compared with three to four
years for a cheap paint. That makes it less expensive per
square foot per year in the long run and easier to maintain.
